public class Solution1137 {
    public int tribonacci(int n) {
        if (n==0) return 0;
        if (n==1) return 1;
        if (n==2) return 1;
        int a=0,b=1,c=1,d;
        for (int i=3;i<=n;i++){
            d=a+b+c;
            a=b;
            b=c;
            c=d;
        }
        return c;
    }

    public static void main(String[] args) {
        System.out.println(new Solution1137().tribonacci(25));
    }
}
